JP3524748B2 - Method for producing sintered cadmium negative electrode - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a nickel - relates manufacturing method of sintered cadmium negative electrode for use in cadmium battery.

[0002]

2. Description of the Related Art Conventionally, a cadmium negative electrode used in a nickel-cadmium storage battery is a sintering type in which a negative electrode active material made of cadmium oxide or cadmium hydroxide is filled in a porous sintered substrate formed by sintering nickel powder. Negative electrode,
There is a non-sintered negative electrode in which a negative electrode active material made of cadmium oxide or cadmium hydroxide is kneaded with a synthetic fiber, a paste and the like to form a paste and applied on a conductive core (substrate) such as punching metal. Among these, the sintered negative electrode, the conductive matrix of the porous sintered substrate is present in the electrode, since the negative electrode active material directly contacts the porous sintered substrate, excellent in conductivity, and, It has been widely used as a power source for various portable devices because of its high rate charge / discharge characteristics and good oxygen gas absorption performance.

In recent years, there have been increasing demands for higher capacity, large current charge / discharge characteristics and longer life of alkaline storage batteries, and various improvements have been made to meet these demands. For example, to increase the capacity, increase the packing density of the active material,
Alternatively, the purpose has been achieved by thinning the separator for separating the positive and negative electrodes.

However, when the active material is packed at a high density to increase the capacity, the space (remaining space) for holding the electrolytic solution in the electrode is occupied by the active material and should be held in the electrode. The amount of electrolytic solution will be reduced. Therefore, the amount of the active material in contact with the electrolytic solution is reduced, and it becomes difficult to smoothly proceed the charge / discharge reaction at the negative electrode, and as the charge / discharge cycle progresses, metal cadmium that cannot be discharged is accumulated. Become.

As a result, there arises a problem that the oxygen gas absorption performance is lowered, or the active material utilization rate is lowered, so that the charge / discharge characteristics are deteriorated. Therefore, both high capacity and large current charge / discharge characteristics are required. It is very difficult to satisfy. Also, as the charge and discharge cycle is repeated,
The surface of the charged metal cadmium is densely covered with the discharged cadmium hydroxide, so-called clogging of the negative electrode active material occurs, and non-dischargeable metal cadmium accumulates inside the negative electrode, resulting in battery life. There was also a phenomenon of reaching.

Therefore, it is possible to cover the surface of the active material with a film of polyvinyl alcohol (PVA) and then cross-link the polyvinyl alcohol to form a cadmium negative electrode.
-121255. This Japanese Patent Laid-Open No. 63-
In the cadmium negative electrode proposed in Japanese Patent No. 121255, it is possible to prevent a film of cadmium hydroxide, which is a discharge product, from being formed on the surface of metal cadmium which is an active material at the time of discharge, and to prevent water on the surface of metal cadmium. Cadmium oxide is generated non-uniformly, the contact between the metal cadmium inside the cadmium negative electrode and the electrolyte is improved, the increase in the amount of metal cadmium that cannot be discharged is suppressed, the decrease in negative electrode capacity is prevented, and the cycle characteristics are improved. I am trying to let you.

It is also possible to add a polysaccharide or a derivative thereof to the inside of a cadmium negative electrode and cover the surface of the negative electrode active material with the polysaccharide or a derivative thereof.
Proposed in Japanese Patent No. 963. This Japanese Patent Laid-Open No. 63-1959
In the cadmium negative electrode proposed in Japanese Patent Laid-Open No. 63, the number of generated nuclei of cadmium hydroxide deposited on the surface of metal cadmium is suppressed to prevent the cadmium hydroxide particles from becoming fine.

On the other hand, it is necessary to cover the surface of the negative electrode of cadmium with a film of polyvinylpyrrolidone (PVP) and the outside thereof with a film of fluororesin.
It was proposed in the publication. In the cadmium negative electrode proposed in Japanese Patent Application Laid-Open No. 9-45316, PVP, which is a polymer paste, and a fluororesin having water repellency are arranged on the outside of the cadmium negative electrode. In the state where the negative electrode is incorporated in the alkaline storage battery, the PVP layer covers the surface of the cadmium negative electrode, and prevents the cadmium that cannot be discharged from accumulating due to the clogging of the negative electrode active material that is likely to occur during the progress of the charge / discharge cycle. In addition, since a fluororesin having water repellency is also provided, it becomes easy to generate a three-phase interface between the negative electrode active material, the nickel sintered body, the electrolytic solution, and the oxygen gas, and the oxygen gas absorption capacity of the cadmium negative electrode is improved. improves.

[0009]

However, in the cadmium negative electrode proposed in Japanese Unexamined Patent Publication No. 63-12125, since PVA is a hydrophilic paste material, this hydrophilic PVA is used as a cadmium negative electrode. When kept, the contact between the cadmium active material and the alkaline electrolyte becomes good, and the cadmium active material and the alkaline electrolyte chemically react,
It was changed to cadmium hydroxide, which had the adverse effect of promoting self-discharge.

Further, in the cadmium negative electrode proposed in Japanese Patent Application Laid-Open No. 63-195963, in order to prevent the cadmium hydroxide particles from becoming finer, the generation of non-dischargeable metal cadmium can be suppressed, but the discharge generation It is impossible to suppress the migration of cadmium hydroxide, which is a substance, to the surface of the negative electrode.

Further, in the cadmium negative electrode proposed in Japanese Patent Application Laid-Open No. 9-45316, a fluorine resin having water repellency is arranged, so that the oxygen gas absorbing ability of the negative electrode is improved, but PVP is Since it swells in the alkaline electrolyte as the charge / discharge cycle progresses, there arises a problem that the water repellent effect of the fluororesin is reduced.

The present invention seeks to solve the above problems.
Therefore, the purpose is to suppress the accumulation of non-dischargeable metal cadmium that occurs with the progress of the charge-discharge cycle, and to suppress the transfer of cadmium hydroxide, which is a discharge product, to the negative electrode surface, and also the charge state. In order to obtain a cadmium negative electrode having a high capacity and excellent cycle characteristics, it is possible to suppress the self-discharge in which the cadmium active material described above changes into cadmium hydroxide.

[0013]

Means for Solving the Problem and Its Action / Effect The present invention, in order to achieve the above object , comprises an active material filling step of filling a nickel sintered substrate with a cadmium active material ,
Sintered substrates filled with cadmium active material are coated with polyvinyl
Loridone, polyvinyl alcohol, vinylpyrrolidone or
Is at least one of the vinyl alcohol copolymers
A step of impregnating or applying one of them, and the copolymer
After drying the sintered substrate impregnated or coated with,
The copolymer existing on the surface of the sintered substrate is polished and removed.
And the removal step, in which the copolymer is removed.
On the surface of the aforesaid sintered substrate, fluororesin discharge
Saddle type consisting of the process of coating and then drying
This is a method for manufacturing a negative electrode of miium .

[0014]

[0015]

[0016]

[0017]

Sintered Cadmium Negative Electrode According to the Present Invention
In the method of manufacturing, after impregnation or coating and drying the copolymer, after removing the copolycondensation <br/> case body is present on the surface of the anode by the removal process, applying a fluororesin dispersion onto the surface of the negative electrode When so as to, the front surface of the cadmium negative electrode
Water repellency is imparted is inhibited the parent aqueous. As a result,
Transition to the surface of the negative electrode of cadmium hydroxide is the discharge product
Cadmium hydroxide crystals are coarsened I accompanied to, this coarsening
The grown crystal grows perpendicular to the separator
It can be suppressed. In addition, since the self-discharge caused by the contact between the cadmium active material and the alkaline electrolyte can be suppressed by the water-repellent effect imparted to the surface of the negative electrode, a high-capacity and long-life alkaline storage battery can be obtained.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION 1. Preparation Example of Cadmium Negative Electrode Plate After forming a nickel sintered porous body (porosity 80%) on the surface of an electrode plate core made of punching metal, a predetermined amount of cadmium active material was added by a chemical impregnation method to the nickel sintered porous body. To fill. That is, after impregnating the sintered nickel porous body with cadmium nitrate, performing an alkali treatment and generating cadmium hydroxide several times, a predetermined amount of cadmium active material (mainly composed of cadmium hydroxide) A negative electrode active material) is filled in a nickel sintered porous body.

Then, the electrode filled with the active material is treated with an alkaline aqueous solution (for example, potassium hydroxide aqueous solution (KO
H)), and formed by charging and discharging,
After securing a predetermined amount of pre-charge (pre-charge) by partial charge, it is washed with water and dried to form a base negative electrode.

This base negative electrode is made of polyvinyl alcohol having a degree of polymerization of 500 with respect to 100 parts by weight of water (PVA (trade name: manufactured by Kuraray Poval, manufactured by Kuraray), hereinafter referred to as PVA).
Is soaked in an aqueous PVA solution in which 6 parts by weight of is dissolved for 60 seconds. By this immersion step, the base negative electrode is impregnated with PVA. After impregnating the base negative electrode with PVA, the base negative electrode is pulled up from the PVA aqueous solution and then completely dried at 80 ° C. Then, the surface of the electrode plate is polished with a wire-containing brush at a pressure of 0.5 to 1.0 Kgf / cm ² .

Then, water 10 is applied to the surface of the base negative electrode.
An aqueous solution (fluorine resin dispersion) in which 5 parts by weight of polytetrafluoroethylene (PTFE: trade name Lubron, manufactured by Daikin Industries, Ltd.) was dispersed with respect to 0 parts by weight was applied, and then dried to obtain the cadmium negative electrode of the example ( The negative electrode a) is produced.

Comparative Example 1 The above-mentioned base negative electrode was polymerized to a polymerization degree of 5 with respect to 100 parts by weight of water.
6 parts by weight in a PVA aqueous solution prepared by dissolving 6 parts by weight of PVA of 00.
Soak for 0 seconds. By this dipping process, P is added to the base negative electrode.
VA is impregnated. Then, after pulling this base negative electrode from the PVA aqueous solution, it is completely dried at 80 ° C. Then, in the same manner as in the example, the electrode plate surface is polished with a wire-containing brush at a pressure of 0.5 to 1.0 Kgf / cm ² to prepare a cadmium negative electrode plate (negative electrode b) of Comparative Example 1.

Comparative Example 2 The above-mentioned base negative electrode was used in a polymerization degree of 5 with respect to 100 parts by weight of water.
6 parts by weight in a PVA aqueous solution prepared by dissolving 6 parts by weight of PVA of 00.
Soak for 0 seconds. By this dipping process, P is added to the base negative electrode.
VA is impregnated. After impregnating the base negative electrode with PVA,
After pulling up the base negative electrode from the PVA aqueous solution, it is completely dried at 80 ° C. Then, on the surface of the base negative electrode impregnated with PVA and dried, 5 parts by weight of polytetrafluoroethylene (PTFE: trade name Lubron, manufactured by Daikin Industries) was dispersed in 100 parts by weight of water in the same manner as in the example. The aqueous solution (fluororesin dispersion) thus prepared is applied and then dried to prepare a cadmium negative electrode (negative electrode c) of Comparative Example 2.

2. Production of sealed nickel-cadmium storage battery The three types of a, b and c cadmium negative electrode plates and the sintered nickel positive electrode plate produced as described above were wound so as to face each other with a nylon nonwoven fabric separator interposed therebetween. 3 types of electrode bodies, each of these 3 types of electrode bodies is inserted into an outer can, and then 30 wt% potassium hydroxide aqueous solution (KOH) is poured and sealed, and A, B, C 3 types of nickel-cadmium storage battery (nominal capacity 1900mA
h) was produced.

3. Charge / Discharge Cycle Test Next, using the three types of nickel-cadmium storage batteries A, B, and C manufactured as described above, at room temperature (23
After charging for 1.9A (1C) for 1.5 hours at ± 5 ° C, charging was suspended for 1 hour, then 1.9A (1C).
Is discharged until the battery voltage becomes 1 V, and the discharge is stopped for 1 hour. When such a charge / discharge cycle was repeated and a charge / discharge cycle test was conducted with the cycle life as the number of cycles until the battery capacity decreased to 60% of the nominal capacity, the results shown in Table 1 below were obtained. .

[0027]

[Table 1] As is clear from Table 1 above, the number of charge / discharge cycles of the battery A (battery using the cadmium negative electrode a of the example) was the same as that of the battery B (battery using the cadmium negative electrode b of the comparative example 1) and battery C (comparison). It can be seen that the number of charge and discharge cycles is larger than that of the battery using the cadmium negative electrode c of Example 2). This is because part of the surface of the cadmium negative electrode is impaired in hydrophilicity and water repellency is imparted to the surface of the cadmium negative electrode.
As shown in FIG. 1 (FIG. 1 is an electron micrograph showing the state of the negative electrode surface after charging / discharging of battery A), the transfer of cadmium hydroxide, which is a discharge product, to the negative electrode surface on the surface of the negative electrode of cadmium. It can be considered that this is because the coarsening of the cadmium hydroxide crystal caused by this transition and the growth of this crystal in the direction perpendicular to the separator were suppressed.

On the other hand, as shown in FIG. 2 (note that FIG. 2 is an electron micrograph showing the state of the negative electrode surface of the battery C after charging and discharging), the batteries B and C are water, which is a discharge product. Cadmium oxide migrates to the surface of the negative electrode, and along with this migration, the crystals of cadmium hydroxide coarsen, and the crystals grow in the direction perpendicular to the separator.

This is the same as Battery B on the surface of the negative electrode.
If E is not applied, water repellency is not imparted to the surface of the negative electrode, so that the migration of cadmium hydroxide to the surface of the negative electrode and the coarsening of the cadmium hydroxide crystals caused by this migration, and the vertical direction with respect to the separator It is considered that the crystal growth is not suppressed. Also, the battery C
If PVA on the surface of the negative electrode is not partially removed as described above, sufficient water repellency cannot be exhibited even if PTFE is applied onto the surface of the negative electrode. Therefore, as in Battery B, the migration of cadmium hydroxide to the surface of the negative electrode and It is considered that this is because the cadmium hydroxide crystal is coarsened due to the migration and the growth of the crystal in the direction perpendicular to the separator is not suppressed.

4. Storage characteristic test Using the three types of nickel-cadmium storage batteries A, B, and C produced as described above, charging was performed for 1.5 hours at a charge flow of 1.9 A (1 C) at room temperature (23 ± 5 ° C)
After 28 days of storage, the battery was discharged with a discharge current of 380 mA (0.2 C) until the battery voltage reached 1 V, and the battery capacity was measured from the discharge time. The results are shown in Table 2 below.

[0031]

[Table 2] As is clear from Table 2 above, the battery capacity after storage of battery A (battery using the cadmium negative electrode a of the example) is battery B
It can be seen that it is larger than the battery capacities after storage (battery using the cadmium negative electrode b of Comparative Example 1) and battery C (battery using the cadmium negative electrode c of Comparative Example 2). This is because part of the surface of the cadmium negative electrode is impaired in hydrophilicity, and the surface of the cadmium negative electrode is provided with water repellency, which suppresses contact of the metal cadmium in the charged state with the electrolytic solution and self-discharge. It can be considered that it was suppressed.

On the other hand, as in the case of battery B, the negative electrode surface is coated with PTFE.
It is considered that since the water repellency is not imparted to the surface of the negative electrode unless C. is applied, the metal cadmium in the charged state often comes into contact with the electrolytic solution, which promotes self-discharge and deteriorates the storage characteristics. In addition, as in battery C, P on the negative electrode surface
It is considered that if VA is not partially removed, even if PTFE is applied on the VA, the water repellency cannot be sufficiently exhibited, so that self-discharge is promoted like the battery B and the storage characteristics are deteriorated.

As described above, in the present invention, by retaining the water repellency on the surface of the negative electrode of cadmium, the migration of the discharge product cadmium hydroxide to the surface of the negative electrode is suppressed, and at the same time with respect to the separator. Since the crystals of cadmium hydroxide are prevented from coarsening in the vertical direction, it is possible to prevent the positive and negative electrodes from being short-circuited, and a long-life alkaline storage battery can be obtained. Further, if water repellency is maintained on the surface of the cadmium negative electrode, contact of metal cadmium in a charged state with the electrolytic solution is suppressed, self-discharge is also suppressed, and storage characteristics are improved.

In the above-mentioned embodiment, only the example of using the copolymer of polyvinyl alcohol (PVA) has been described. However, in addition to PVA, a copolymer of polyvinylpyrrolidone (PVP), vinylpyrrolidone or vinyl alcohol. It has been confirmed that similar results can be obtained by using.

Further, in the above-described embodiment, an example in which the cadmium negative electrode is dipped in the PVA aqueous solution to impregnate the cadmium negative electrode with PVA has been described. However, even if the cadmium negative electrode is coated with the PVA aqueous solution, the same result is obtained. We confirm that the results can be obtained. Further, in the above-described embodiment, an example in which polytetrafluoroethylene (PTFE) is used as the fluororesin has been described, but the same effect can be obtained as long as the fluororesin has water repellency.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing a state of a negative electrode surface after a charge / discharge cycle of a cadmium negative electrode of the present invention.

FIG. 2 is an electron micrograph showing a state of a negative electrode surface after a charge / discharge cycle of a cadmium negative electrode of a conventional example (comparative example).

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masataka Shinyashiki 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-4-79160 (JP, A) JP Sho 63-202857 (JP, A) JP 4-19963 (JP, A) JP 3-1442 (JP, A) JP 6-243863 (JP, A) JP 61-147455 (JP , A) JP-A-1-239766 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/24 H01M 4/26 H01M 4/62

Claims (2)

(57) [Claims] 1. An active material filling step of filling a nickel sintered substrate with a cadmium active material, and a polyvinyl pyrrolidone, polyvinyl alcohol, vinylpyrrolidone or a copolymer of vinyl alcohol on the sintered substrate filled with the cadmium active material. A step of impregnating or applying at least any one of them, and the copolymer existing on the surface of the sintered substrate after drying the sintered substrate impregnated or applied with the copolymer
A removal step of removing by polishing, the sintered Yuimoto said copolymer in the removing step is removed
Sintered type method for producing a cadmium negative electrode comprising a step of <br/> dried after coating the fluororesin dispersion onto the surface of the plate. 2. The surface of the sintered substrate in the removing step
The copolymer present is polished by a wire entering brush
The method for producing a sintered cadmium negative electrode according to claim 2, characterized in that the negative electrode is removed .